Differences in the organization of adenovirus E1A promoters are not important for their full activity.

The 5'-E1A control regions of adenovirus (Ad) types 2, 3 and 12 were cloned upstream from the cat gene. Each serotype was characterized by unique organization of the 5'-E1A non-coding region. All three 5'-non-coding E1A regions were able to stimulate the cat gene transcription in HeLa cells. Hybrid plasmids between Ad2/Ad3 and Ad2/Ad12 revealed the same level of CAT activity as the native plasmids but the optimum activity of promoter was achieved only when its organization was not modified. These observations suggest that various nuclear factors take part in the activation process of each promoter.